It's all preference. I NEVER flip to my clean channel. It's actually used as my mute button to kill the hum during testimonies and stuff.
I, personally, set my amp gain at the dirtiest that I would need, then I back off my guitar volume to adjust the grit. I think this was posted before, I can't remember by who, though.
I'll see if I can find it, there was a big discussion on it.